1. Field of the Invention
The present invention relates to an image stabilization control circuit embedded in an imaging apparatus.
2. Description of the Related Art
In recent years, imaging apparatuses, such as digital still cameras and digital video cameras, have realized high image quality through increases in the number of pixels of their built-in image sensors. On the other hand, as another method for imaging apparatuses to achieve higher image quality, it is desirable for an imaging apparatus to provide an anti-shake function to prevent shaking of a subject caused by shaking of a hand holding the imaging apparatus.
More specifically, an imaging apparatus is provided with a detection sensor, such as a gyro sensor, to prevent shaking of a subject by driving an optical component, such as a lens or an image sensor, in accordance with an angular velocity component created by vibration of the imaging apparatus. As a result, even if the imaging apparatus vibrates, a vibration component is not reflected in an obtained picture signal so that a picture signal having high image quality without blurring can be obtained.
FIG. 4 shows a block diagram of a conventional image stabilization control circuit 100 utilized for realizing an anti-shake function. The image stabilization control circuit 100 is provided in the imaging apparatus and operates in accordance with control of a main control circuit (not shown) provided in the imaging apparatus. The image stabilization control circuit 100 is connected to a position detector 102, a lens driver 104, and a vibration detector 106.
The position detector 102 detects the position of a lens used in the imaging apparatus. The position detector 102 can be implemented with a Hall device to generate an induced current according to the absolute position of the lens and output a voltage signal. The lens driver 104 can be implemented with a voice coil motor. The image stabilization control circuit 100 controls the position of a moving coil of the voice coil motor, namely, the position of the lens, by adjusting the voltage value supplied to the lens driver 104. The lens driver 104 drives the lens at a vertical in-plane with respect to the optical axis of the imaging apparatus. The vibration detector 106 detects vibration of the imaging apparatus and outputs the result to the image stabilization control circuit 100. The vibration detector 106 can be implemented with a gyro sensor. An angular velocity signal is generated according to the vibration that was applied to the imaging apparatus and output to the image stabilization control circuit 100.
It is preferable to configure the position sensor 102, the lens driver 104, and the vibration detector 106 each from at least two devices. For example, multiple devices are provided corresponding to a horizontal component and a vertical component in a plane perpendicular to the optical axis of the imaging apparatus for detecting lens position, moving the lens, and detecting vibration of the imaging apparatus.
Next, the image stabilization control circuit 100 will be described in detail. The image stabilization control circuit 100 includes a servo circuit 10, a lens driver circuit 12, an analog-to-digital converter (ADC) 14, a CPU 16, and a digital-to-analog converter (DAC) 18.
The servo circuit 10 generates a signal for controlling the lens driver 104 in accordance with a voltage signal output from the position detector 102. The servo circuit 10 is configured to include an analog filter circuit, which may include externally connected resistors and capacitors, and generates a signal to control the lens driver 104 so that the optical axis of the lens and the center of the image sensor provided in the imaging apparatus coincide. The lens driver circuit 12 generates a lens driving signal to drive the lens driver 104 on the basis of the signal output from the servo circuit 10.
The ADC 14 converts the analog angular velocity signal that is output by the vibration detector 106 into a digital signal. The CPU 16 generates an angular signal indicating a movement amount of the imaging apparatus on the basis of the digital angular velocity signal. The CPU 16 is connected to memory (not shown) and performs processing for generating the angular signal on the basis of software stored in the memory. The DAC 18 converts the digital angular signal generated by the CPU 16 into an analog signal.
Here, the servo circuit 10 generates a lens driving signal to drive the lens driver 104 in accordance with a signal, in which the analog angular signal output by the DAC 18 and the voltage signal output from the position detector 102 are added. Namely, to prevent subject shaking due to hand shake, shaking of the subject image on the image sensor is suppressed by varying the position of the lens on the basis of the angular signal indicating the movement amount of the imaging apparatus. Thus, shaking of the subject image due to hand shake is suppressed so that a picture signal having high image quality can be obtained.
To improve the processing speed of the image stabilization control circuit, it is desirable to replace the servo circuit, lens driver, and vibration detection signal processing circuit with logic circuits capable of digital processing. Furthermore, since the image stabilization control circuit is to be embedded in an image sensor or a lens module for an image sensor, such as of a digital camera, miniaturization as much as possible is necessary also when converting to logic circuits.
Furthermore, it is preferable for the output signal of the position detector used in position detection of a driven section, such as a lens, to be proportional in strength to the amount of deviation from a reference position. Generally, however, as shown in FIG. 5, the output signal of the position detector is not proportional in strength to the amount of deviation from the reference position. Although it is therefore necessary to perform processing for linear compensation for the output signal of the position detector at the image stabilization control circuit, embedding a compensation circuit as fixed logic circuitry is difficult due to variations in characteristics among individual position detectors.